Description and examples of Brain SPECT and MUGA scans.
In cases where a stroke has been confirmed and an image is needed to determine
the location and extent of the stroke, brain perfusion SPECT images are
frequently required. Brain perfusion SPECT imaging can be performed with
two different 99mTc agents, 99mTc-HMPAO (Ceretecr) or 99mTc-ECD (Neuroliter).
99mTc-ECD is frequently preferred over 99mTc-HMPAO, due to more rapid brain
uptake and blood clearance, which allows for increased stability, and therefore
better imaging, over 99mTc-HMPAO. The peak amount of activity that is taken
up in the brain is usually around 5 to 7 percent of the dose administered;
due to this poor localization, a dose of 20-30 mCi is required. Imaging
should be performed between 30 and 60 minutes after the injection. The
dose is stable and may be used for up to six hours after preparation. Patients
should be urged to void frequently and to drink fluids after the scan is
performed to allow for rapid removal of the 99mTc from the bladder, the
primary site of localization.
In cases where the ejection fraction (EF) of a patient with compromised
heart function needs to be determined, such as in congestive heart failure,
a Multiple Gated Aquisition (MUGA) scan is usually required. The MUGA scan
involves the labeling of red blood cells (RBCs) with 99mTc, with a typical
dose of 10 to 20 mCi; these labeled RBCs can be detected in the circulation
and give good images of the pumping heart in motion. A left anterior oblique
view can be obtained with a gamma camera; this can be used to distinguish
left ventricular function from right ventricular function. The determination
of EF can be determined using the formula EF = (end diastolic volume -
end systolic volume)/(end diastolic volume - background). The patient is
usually scanned at rest and under either physiologic or pharmacologic stress.
The result of these are compared to determine the type and severity of
Two different methods of labeling can be employed, the in vivo
method and the in vitro method. The in vitro method involves removing 1
to 3 ml of the patient's blood. Stannous chloride is added to the blood;
it accumulates inside the RBCs. The 99mTc is then added in the form of
99mTc-sodium pertechnetate. The 99mTc-pertechnetate enters the RBC and
is reduced by the stannous chloride, which prevents it from diffusing back
out of the cell. The blood is then reinjected into the patient. The in
vivo method requires the stannous chloride to be injected into the patient
first. After a period of about 20 minutes, the 99mTc-pertechnetate is injected
into the patient. Although the in vivo method is easier to perform, it
does require two injections, and labeling efficiency can not be definitively
Examples of Brain SPECT images using 99mTc-ECD and a Multiple Gated Aquisition
(MUGA) using in vivo RBC labelling with 99mTc are included below.
1. The first case is a Brain SPECT scan using 30 mCi 99Tc-ECD. This scan
illustrates the effects of chronic alcohol abuse. The scan shows decreased
blood flow to the cerebral cortex at the bilateral parietal lobes. Notice
that the parietal lobes are affected while sparing the rest of the brain.
This is typical of chronic substance abuse.
2. This scan was performed using 29mCi of 99mTc-ECD. The scan shows
decreased perfusion in the frontal, parietal, and temporal lobes. This
is typical of patients with ischemic brain disease secondary to stroke.
3. This scan was carried out using 99mTc-ECD. It shows the typical pattern
of atrophy found in Alzheimer patients. It can be distinguished from the
ischemic disease scan by following up with a scan performed following a
Diamox injection. If the perfusion improves, it is more than likely an
Alzheimer type disorder. If the infarcted areas become worsened, it would
suggest an ischemic disorder.
4. This scan is a MUGA scan using in vivo labelling of the red blood
cells with 99mTc. The scan showed the left ventricle to be enlarged with
global hypokinesis especially in the inferioapical region. This patient
had an ejection fraction of 25%. The patient was 47 years old and had a
history of CAD.
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